A plurality of types of balanced-unbalanced transformation device have been proposed that perform balanced-unbalanced conversion by having one ½ wavelength resonator and two ¼ wavelength resonators formed on a dielectric substrate.
FIG. 1 illustrates the structure of a balanced-unbalanced transformation device described in Patent Document 1. A balanced-unbalanced transformation device 101 includes a plurality of laminated dielectric substrates. The balanced-unbalanced transformation device 101 further includes a ground terminal (not shown) on each of an upper side surface A and a lower side surface B thereof, an unbalanced terminal (not shown) on a left side surface C thereof, and two balanced terminals (not shown) on a right side surface D thereof. As shown in the drawing, an unbalanced pattern 102 is formed on a major surface of the uppermost dielectric substrate layer. The unbalanced pattern 102 serves as an electrode of a ½ wavelength resonator. In addition, a balanced pattern 103A and a balanced pattern 103B are formed on the lowermost dielectric substrate layer. The balanced pattern 103A and the balanced pattern 103B serve as electrodes of different ¼ wavelength resonators.
The unbalanced pattern 102 is an electrode that is substantially U shaped. The unbalanced pattern 102 includes line portions 102A and 102B disposed parallel to each other, a line portion 102C that connects the line portion 102A to the line portion 102B, a lead-out electrode 102D used for connection with the ground electrode, and a lead-out electrode 102E used for connection with the unbalanced terminal. Each of the balanced patterns 103A and 103B is an electrode pattern that is substantially I shaped. The line portions 102A and 102B of the unbalanced pattern 102 face the balanced pattern 103A or 103B with a first dielectric substrate therebetween.
The balanced-unbalanced transformation device 101 converts an unbalanced signal input to the unbalanced terminal into first and second balanced signals, and outputs a first balanced signal from one of the balanced terminals. In addition, the balanced-unbalanced transformation device 101 outputs, from the other balanced terminal, a second balanced signal having a phase substantially opposite to that of the first balanced signal.
When, conversely, a balanced signal is input to the two balanced terminals, the balanced-unbalanced transformation device 101 converts the balanced signal into an unbalanced signal, and outputs the unbalanced signal from the unbalanced terminal.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 10-290107
In general, the performance of a balanced-unbalanced transformation device is evaluated by using the width of a frequency range in which the phase difference and the amplitude difference between two balanced signals are within desired ranges.
However, in the balanced-unbalanced transformation device described in Patent Document 1, the shape of the unbalanced pattern 102 and the arrangement of the balanced patterns 103A and 103B are asymmetrical. Accordingly, the frequency range in which a desired balancing characteristic is provided is disadvantageously narrow.